Fix a Harbormaster build issue with new URI code

Summary: Ref T10748. We're returning a `PhabricatorRepositoryURI` here but the code expects an actual `PhutilURI`.

Test Plan:
This should clear this up in production:

```
Daemon 180278 STDE [Wed, 04 May 2016 23:25:16 +0000] [2016-05-04 23:25:16] EXCEPTION: (PhutilProxyException) Error while executing Task ID 1677075. {>} (RuntimeException) Object of class PhabricatorRepositoryURI could not be converted to string at [<phutil>/src/error/PhutilErrorHandler.php:205]
Daemon 180278 STDE [Wed, 04 May 2016 23:25:16 +0000] arcanist(head=master, ref.master=c58f1b9a2507), libcore(), phabricator(head=master, ref.master=29d1115037b8), phutil(head=master, ref.master=0709cd5cfc26), services(head=master, ref.master=04ae8c8f8e3b)
Daemon 180278 STDE [Wed, 04 May 2016 23:25:16 +0000]   #0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer, array) called at [<phabricator>/src/applications/repository/storage/PhabricatorRepository.php:1200]
Daemon 180278 STDE [Wed, 04 May 2016 23:25:16 +0000]   #1 <#2> PhabricatorRepository::getPublicCloneURI() called at [<phabricator>/src/applications/repository/storage/PhabricatorRepositoryCommit.php:395]
```

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10748

Differential Revision: https://secure.phabricator.com/D15844

src/applications/repository/storage/PhabricatorRepository.php

@@ -1292,7 +1292,7 @@ final class PhabricatorRepository extends PhabricatorRepositoryDAO
       return null;
     }
 
-    return head($clone_uris);
+    return head($clone_uris)->getEffectiveURI();
   }
 
   private function getRawHTTPCloneURIObject() {